I just finished NiBiRu, and I have to say that I found the gameplay acceptable (no unfair puzzles), the storyline was good (except as noted below), there were no unwieldy "action" sequences, BUT there were a number of instances of pixel hunting, some of which were extreme. There also were a number of instances where I had to keep wandering from screen to screen, waiting for the game to catch up so that some key sequence would appear (apparently time triggered)... This is nothing but poor game design, which I thought had been left behind by game designers long ago.

I also did not like the GUI, with it's strange, non-intuitive in-game functions for the right & left mouse buttons.

It is the game's ending which holds the biggest dissappointment.. Once again, the game's makers apparently could not think of a suitable ending which would resolve the outstanding questions in the adventure, so they just stopped the gameplay, and threw in a totally unacceptable cutscene which did VERY little to explain what happened to "end" the game..

In game, the right mouse button is not assigned to bring up your inventory, nor change your action type (either of these actions is more or less accepted gaming practice).

In this game, the right mouse button is used to sometimes "look" closer at something (This does not always work, and is frankly confusing).
Further, within the actual puzzles themselves, the right mouse button controls different aspects of some of the puzzles, and frankly I found it very confusing when working out a puzzle to try and remember that the right mouse button performs a different action in the puzzle than the left button, and to remember to use the right button...

The use of the right mouse button was not at all intuitive.

The ending was very disappointing. It seemed to be tacked-on at the last minute; It seemed like the game play was not really finished, but they ran out of room on the cds, or money, or something... The ending left far too much of the quest unexplained, imho

What disappointed me most about NiBiRu was it's plot, but what made it so disappointing was the protagonist - Martin Holan.

SPOILERS

Martin has no personality at all, no clear past (other than he works in the same profession as his uncle) no family we know of other than said uncle, no friends, no hobbies, no positive or negative traits, and the only things clear about him is that he has no interest in the supposedly incredible plot he is uncovering:

He finds ancient artefacts, underground nazi laboratories with interesting experiments, he meets an old man who must've used some unnatural means to reach such and old age, he is nearly killed about four times, he sees murdered people, and sometimes sees their killer, his uncle is murdered at one point as well, he sees an alien and a strange alien artefact, and HE DOESN'T SEEM TO CARE!

All of these incredible happenings are not met with any response, Martin shows no interest whatsoever. So what should've been an interesting investigation with great findings turns to be no more than Martin's 'programming'. When his uncle dies he doesn't show any sadness, and barely explains why he is keeping on with his quest.
After nearly being killed and escaping he doesn't really show any sign of panic, or concern about nearly dying (nor does he care when he injures someone, disturbs and lies to an old man, or when he kills a helpless animal).
Strangely, the only time he shows emotion is when he needs to pay for something, and then he is annoyed for wasting time and money.
Part of the reason the ending is so disappointing is because Martin sees a friggin' alien and barely even looks at it!

Regarding the voice acting (which you are taking exception to here).. I am somewhat hearing impaired, and I don't pay all that much attention to the voice acting in many games (I always turn on subtitles).. Usually there is background music, etc., which makes the voice acting difficult for me to understand (some games will allow you to adjust the music and sound effects separately from the voice, which is a great boon for me).

Also, being a long time adventure gamer, I do not expect voice acting in adventure games to be of particularly high quality, as it traditionally was not (At the begining we were thrilled to have graphics to go with the text).